The current trend in refinery crude slates is for the utilization of increasingly heavy and "dirty" feedstocks, including large amounts of sulfur, nitrogen, metals, etc. In addition, an increasing proportion of these crude oils is present as residual fuels, and the principal outlet for these fuels is as low sulfur fuel oils subsequent to catalytic desulfurization. Because of the increasing problems of air pollution, particularly with regard to sulfur oxide emissions, increasing concern among refiners has arisen with respect to the utilization of these feedstocks. Consequently, the development of efficient and economical means for sulfur removal from these heavy sulfur-bearing oils has become a primary research goal in this industry. While the most practical desulfurization process at this time is the catalytic hydrogenation referred to above, these processes generally produce a product which, while having reduced sulfur and nitrogen content, includes sufficient feedstock impurities to render further processing, particularly by way of catalytic cracking, increasingly difficult if not impossible. The use of catalytic cracking, however, is today the principal gasoline manufacturing process in a modern refinery. Furthermore, the catalytic cracking catalysts which are generally employed are quite sensitive to these catalyst poisons, such as sulfur, etc., and additionally sulfur dioxide emissions must be dealt with upon regeneration of these deactivated catalysts. Also, the nitrogen compounds present in these feedstocks tend to neutralize the required catalyst acidity, and favor the lay-down of coke on the catalyst surface. Furthermore, Conradson carbon precursors generate surface coke, the excess formation of which upsets the heat balance of the catalytic cracking process. Finally, the metals present in these feedstocks, primarily nickel, further cause catalyst deactivation.
On the other hand, the catalytic hydrogenation process itself, while generally quite efficient in handling distillates, becomes much more complex and expensive, and considerably less efficient, as these feedstocks become increasingly heavy, e.g., whole or topped crudes and residua. Many of the same contaminants which render the hydrogenation products difficult to utilize in catalytic cracking processes thus have a similar effect on the hydrogenation catalyst itself. Furthermore, much of the sulfur contained in the higher molecular weight molecules in these feedstocks can only be broken down when operating under severe operating conditions. These same conditions, however, also tend to accelerate catalyst deactivation due to accelerated coke and metal deposition on the catalyst surfaces.
It has long been known that alkali and alkaline earth metals, as well as their corresponding hydrides, hydroxides, oxides, etc., exhibit desulfurization activity for residua. Even so, however, these compounds have been found to suffer from several distinct drawbacks, such as poor desulfurization efficiency, a tendency to produce oil insoluble sludges, the inability to upgrade feedstocks by demetallization, and the formation of salt-oil mixtures that are exceedingly difficult to resolve by conventional means. Furthermore, again, none of these materials has ever been employed to obtain the simultaneous desulfurization and substantial hydroconversion of the feedstocks being treated. In this regard, however, the assignee of the present application, Exxon Research and Engineering Company, has recently discovered that such simultaneous desulfurization and hydroconversion of these feedstocks can be obtained by utilizing various alkali and alkaline earth metal compounds under certain conditions. Thus, in Ser. No. 571,904, filed on Apr. 28, 1975 abandoned for ClP 733,085, the inventors of the present application discovered that alkaline earth metal hydrides and alkaline earth metal oxides can be employed for such purposes under increased hydrogen partial pressures. Furthermore, in Ser. No. 571,903, also filed on Apr. 28, 1975 now U.S. Pat. No. 4,076,613, the inventor, Roby Bearden, Jr. discloses the use of alkali metals for such combined desulfurization and hydroconversion, obtaining at least 50 weight percent sulfur reduction as well as a reduction of the 1050.degree. F.+ fraction as well as a significant decrease in the Conradson carbon and an increased API gravity of the hydrogenated products. In addition, in U.S. Pat. No. 3,976,559 the inventors, Roby Bearden, Jr. and Glen R. Hamner, disclose a combined hydrodesulfurization and hydroconversion process including initial contact with a hydrodesulfurization catalyst which selectively avoids converting the asphaltene agglomerates in metal-containing compounds therein, and subsequent contact with an alkali metal for combined desulfurization and hydroconversion to lower boiling products. Finally, in U.S. Pat. No. 4,003,823 the inventors, William C. Baird, Jr. and Roby Bearden, Jr., disclosed the combined desulfurization and hydroconversion of heavy carbonaceous feeds by contacting with alkali metal hydroxides, at elevated temperatures, in the presence of added hydrogen.
Each of these processes, all of which are assigned to Exxon Research and Engineering Company, the assignee of the present invention, provides an excellent commercial possibility for the simultaneous hydroconversion and hydrodesulfurization of heavy sulfur-containing feedstocks.
It has now been found, in addition, that various alkali metal and alkaline earth metal compounds, and mixtures thereof, may be advantageously employed for the simultaneous desulfurization and hydroconversion of various sulfur-containing petroleum oil feedstocks which have been previously subjected to catalytic desulfurization in the general manner described above. It has also been discovered that various mixtures of alkali metal and alkaline earth metals and compounds thereof may be employed for the significant combined desulfurization and hydroconversion of various heavy sulfur-containing feedstocks.